In the field of process measurements and automation technology, often used for highly accurate measurement of physical parameters, parameters such as e.g. mass flow, density and/or viscosity, of a medium, for example a gas and/or a liquid, are measuring systems formed by means of at least one inline measuring device. These measuring systems apply a measuring transducer of vibration type, through which the medium flows, and a measuring and operating circuit connected thereto, to bring about, in the medium, reaction forces, such as e.g. Coriolis forces, corresponding to mass flow, inertial forces corresponding to density, or frictional forces corresponding to viscosity, etc., and, derived from these forces, to produce a measurement signal representing, respectively, mass flow, viscosity and/or density of the medium. Such inline measuring devices with a measuring transducer of vibration type, as well as their manner of operation, are known per se to those skilled in the art and are described extensively and in detail in e.g. WO-A 03/095950, WO-A 03/095949, WO-A 02/37,063, WO-A 01/33,174, WO-A 00/57,141, WO-A 99/39,164, WO-A 98/07,009, WO-A 95/16,897, WO-A 88/03,261, US 2003/0208325, U.S. Pat. Nos. 6,910,366, 6,895,826, 6,880,410, 6,691,583, 6,651,513, 6,513,393, 6,505,519, 6,006,609, 5,869,770, 5,861,561, 5,796,011, 5,616,868, 5,602,346, 5,602,345, 5,531,126, 5,359,881, 5,301,557, 5,253,533, 5,218,873, 5,069,074, 4,957,005, 4,895,031, 4,876,898, 4,733,569, 4,660,421, 4,524,610, 4,491,02, or U.S. Pat. No. 4,187,721. For conveying the flowing medium, the measuring transducers include, in each case, at least one measuring tube held in a support frame (most often formed as a closed transducer housing) and having a bent or straight, tubular segment, which, during operation, is caused to vibrate, driven by an electromechanical exciter mechanism, for producing the above-mentioned reaction forces. For registering vibrations of the tubular segment, especially vibrations at its inlet and outlet sides, the measuring transducer has, additionally, in each case, a sensor arrangement reacting to movements of the tubular segment.
In the case of Coriolis mass-flow measuring devices, it is known that the measurement of the mass-flow of a medium flowing in a pipeline rests on the fact that the medium is allowed to flow through the measuring tube inserted into the pipeline and oscillating during operation at least partially laterally to a measuring tube axis, this leading to Coriolis forces being induced in the medium. These, in turn, effect that regions of the measuring tube at its inlet side and at its outlet side oscillate shifted in phase relative to one another. The size of these phase shifts serves, in such case, as a measure for the mass flow. The oscillations of the measuring tube are, therefore, registered by means of two oscillation sensors of the aforementioned sensor arrangement spaced from one another along the measuring tube and are converted into oscillation measurement signals, from whose mutual phase shift, the mass flow is derived. Already the above-referenced U.S. Pat. No. 4,187,721 mentions additionally that also the instantaneous density of the flowing medium is measurable by means of such inline measuring devices, this being done taking into consideration a frequency of at least one of the oscillation measurement signals delivered from the sensor arrangement. Moreover, most often, also a temperature of the medium is measured in suitable manner directly, for example by means of a temperature sensor arranged on the at least one measuring tube. Additionally, straight measuring tubes, excited to torsional oscillations about a torsional oscillation axis essentially parallel to the measuring tube longitudinal axis or coinciding therewith, effect that radial, shear forces are produced in the medium conveyed therethrough, whereby the torsional oscillations, in turn, withdraw significant oscillatory energy, which is dissipated in the medium. Resulting therefrom, a significant damping of the torsional oscillations of the oscillating measuring tube occurs, so that, in order to maintain these oscillations, additional electrical exciting power must be fed to the measuring tube. Derived from an electrical exciting power correspondingly required for maintaining the torsional oscillations of the measuring tube, for example, also a viscosity can at least approximately be ascertained by means of the measuring transducer in manner know to those skilled in the art; compare, in this respect, especially also U.S. Pat. Nos. 4,524,610, 5,253,533, 6,006,609 or U.S. Pat. No. 6,651,513. Thus, it can, therefore, be quite evidently assumed in the following that, even when not expressly described, in any case, also density, viscosity and/or temperature of the medium can be measured by means of modern inline measuring devices having measuring transducers of vibration type, especially by means of Coriolis mass flow measuring devices, especially since these parameters are often considered in the measurement of mass flow anyway, for compensating measurement errors resulting from fluctuating density and/or viscosity of the medium; compare, in this connection, especially the already mentioned U.S. Pat. Nos. 6,513,393, 6,006,609, 5,602,346, WO-A 02/37063, WO-A 99/39164 or also WO-A 00/36379. Besides such measuring transducers of vibration-type, also frequently applied in process measurements and automation technology for inline measurements are inline measuring devices with magneto-inductive measuring transducers or measuring transducers evaluating the travel time of ultrasonic waves transmitted in the flow direction, especially also those working according to the Doppler principle. Since the principles of construction and functioning of such magneto-inductive measuring transducers are sufficiently described in e.g. EP-A 1 039 269, U.S. Pat. Nos. 6,031,740, 5,540,103, 5,351,554, 4,563,904, etc., or for such ultrasonic measuring transducers in e.g. U.S. Pat. Nos. 6,397,683, 6,330,831, 6,293,156, 6,189,389, 5,531,124, 5,463,905, 5,131,279, 4,787,252, etc., and, moreover such are likewise sufficiently known to those skilled in the art, a detailed explanation of these measuring principles need not be presented here.
As mentioned, for example, in U.S. Pat. No. 4,957,005, in numerous applications of industrial measurements technology, an important criterion for the operation of inline measuring devices of the described kind is that the flow measuring transducer can be emptied in-situ, thus as installed. Thus, standards, e.g. ASME BPE, established in the foods industry or also in the pharmaceuticals industry, require that line segments must be self-emptyable throughout a broad range of tilts. Accordingly, practically all line segments, including those of the flow transducer, have to have a certain amount of rise, such as to guarantee a self-emptying capability for the pipeline system. The required self-emptying capability can be implemented for a large number of flow measuring transducers in simple manner by selecting for the flow measuring transducer during installation of the inline measuring device a tilt appropriately matched to the actual geometry of the at least one measuring tube, such that, during operation, when allowing the connected pipeline to empty, also a self-emptying of the at least one measuring tube is enabled.
In the use of such inline measuring devices with at least one measuring tube joined into the course of the pipeline conveying medium, it has further been found that, in the case of inhomogeneous media, especially two, or more, phase media, the measurement signals produced therewith can show, to a considerable degree, non-reproducible fluctuations, even though the parameters of the medium, especially the parameter mass flow, significantly influencing the measurement signals are held practically constant; compare, in this connection, also the initially mentioned U.S. Pat. Nos. 6,910,366, 6,880,410, 6,505,519, 6,311,136 or U.S. Pat. No. 5,400,657. As a result of this, these measurement signals in the case of multiphase flows of medium are practically unusable for a highly accurate measurement of the physical flow parameter of interest. Such inhomogeneous media can be, for example, liquids, into which, as e.g. practically unavoidable in the case of metering- or bottling-processes, a gas, especially air, present in the pipeline, is introduced, or out of which a dissolved medium e.g. carbon dioxide, outgasses and leads to foam formation. As further examples of such inhomogeneous media, additionally mentioned should be also emulsions, wet- or saturated-steam, as well as fluids with entrained, solid particles. Especially, it has been determined in the case of inline measuring devices having a measuring transducer of vibration-type, such as also discussed, for example, in JP-A 10-281846, EP-A 1 291 639, U.S. Pat. Nos. 6,880,410, 6,505,519 or U.S. Pat. No. 4,524,610, that the oscillation measurement signals derived from the oscillations of the measuring tube, especially also the mentioned phase shift, are, in the case of two, or more, phase media, subject, to a considerable degree, to fluctuations, despite the fact that the mass flow, as well as also viscosity and density of the individual phases of the medium are held practically constant and/or appropriately taken into consideration, so that they can, without remedial measures, be completely unusable for the measurement of the physical flow parameter of interest.
Causes of the measurement errors associated with the measurement of inhomogeneous media by means of measuring transducers of vibration-type include, for example, one-sided accumulation, or settling internally on the measuring tube wall, of gas bubbles or solid particles entrained in liquids, or the so-called “bubble-effect”, wherein gas bubbles entrained in the liquid act as disturbing bodies for liquid volume elements accelerated transversely to the longitudinal axis of the measuring tube. For lessening the measurement errors associated with two or more phase media, it is proposed, for example, in U.S. Pat. No. 4,524,610, to apply the measuring transducer in a specified installed orientation, in this case essentially vertical, in order to avoid an undesired distribution of disturbing gas bubbles. Besides such disturbing influences as a result of inhomogeneities in the medium, however, also asymmetries in the flow profile, brought about, for example, by curved measuring tubes and/or in the case of turbulent flow, can lead to dependencies of the measurement accuracy on the installed orientation of the measuring transducer.
In view of the need for a defined installed position for flow measuring transducers of the described kind, especially a defined orientation of the flow transducer with reference to a reference axis, be it for reasons of a needed self-emptying capability or for reasons of measurement accuracy, manufacturers of such inline measuring devices make available to the user usually catalogs of suitable, and even unsuitable, installed positions of the respective measuring devices; suitable installed positions are most often limited to those which are essentially vertical and/or horizontal. However, it has been found, in such case, that, especially as regards special applications, in which an, in the above sense, standardized (thus primarily vertical or horizontal) installed position cannot, or should not, be implemented, substantial problems can arise in the assurance of a sufficient measurement accuracy and/or the assurance of a self-emptying of the flow transducer.